When ad platforms provide guidance, it is often taken as absolute truth. The expectation is that their help documentation and support channels offer accurate, actionable advice.
However, despite providing clear guidance after reviewing the findings from Optmyzr’s experiment, Google spent months telling advertisers PMax exclusions would not be respected if they came from the API.
Here’s Google’s previous documentation:
Here’s Google’s answer in their AI overviews:
The same was shared in their communications with advertisers.
This post outlines an experiment conducted to determine if API placement exclusions work for PMax campaigns, contrary to Google’s previous claims.
It’s worth noting that as a result of this experiment, Google did some digging into their own systems and came up with the following response:
As the screenshot shows, this is how to think about placement exclusions:
We’ll also explore what this means for advertisers and how to navigate support discrepancies moving forward.
What we uncovered from our experiment
Details of the experiment
Optmyzr conducted a controlled experiment to test whether placements excluded via the API would be respected for PMax campaigns. Here’s what we did:
1. Setting up the campaign
We launched a brand new PMax campaign in our brand’s ad account on December 30th 2024. We gave the campaign till Jan 13, 2025 to accrue clicks, impressions, and placements.
2. Applying exclusions
Identifying placements we wanted to exclude, we implemented these exclusions through our API connection. The exclusions appeared at the account level, despite Google’s documentation stating that placement exclusions must be done through the UI. We applied these exclusions on Jan 13, 2025.
3. Monitoring the results
No ad spend occurred on the excluded placements as of Jan 21, 2025, proving the API exclusions were effective. The example placement we chose to follow was “Mobile App: Vita Mahjong (iTunes App Store), by VITA STUDIO PTE. LTD.”
This experiment’s results reveal a stark contrast between Google’s official guidance and the platform’s actual functionality.
What are the implications for advertisers?
1. Documentation vs. reality
This finding underscores the importance of questioning and testing platform limitations. While help documentation serves as a baseline, advertisers can no longer treat it as definitive. PMax, as an evolving ad type, requires a proactive approach to testing features and functionalities.
2. Efficiency through the API
Excluding placements via the API is significantly more efficient than using the UI. The UI process involves cumbersome formatting and limitations, which can deter advertisers from making necessary exclusions.
The API’s effectiveness, as demonstrated in our experiment, offers a faster, more scalable alternative.
The miscommunication around how placement exclusions are respected came from the very real issue all SAAS faces: innovation happens faster than support documentation can keep up.
What advertisers should do next
1. Embrace testing
Treat every rule or limitation as an opportunity to test. The findings from this experiment reinforce the need to verify functionality instead of relying solely on documentation.
2. Leverage tools and expertise
If you’re an Optmyzr customer, rest assured that our rule engine and smart exclusions protect your accounts effectively. For non-customers, consider engaging with experts like Nils Rooijmans and Mike Rhodes, who offer many scripting solutions and insights.
3. Active account management
Ensure your accounts are actively monitored. Automated rules are valuable but should not replace ongoing oversight. Regular checks are critical to adapting to platform changes and discrepancies.
A balanced perspective
Despite these challenges, Google remains a meaningful channel for advertisers. Properly applied exclusions and strategic management can yield exceptional results. Optmyzr customers can use our Smart Exclusion tool to quickly identify and exclude wasteful exclusions. We also encourage testing alternatives like Microsoft’s PMax and exploring other platforms.
At Optmyzr, our mission is to safeguard your ad investments. By staying informed and proactive, you can navigate the complexities of digital advertising and adapt to the fast-changing industry
Not an Optmyzr customer yet? Now’s the best time to sign up for a full functionality 14-day free trial.
Thousands of advertisers — from small agencies to big brands — worldwide use Optmyzr to manage over $5 billion in ad spend every year.
You will also get the resources you need to get started and more. Our team will also be on hand to answer questions and provide any support we can.
